Process and apparatus for loading a particulate solid into a vertical tube

ABSTRACT

A process is described in which an elastic fluid is contacted with a particulate solid. This comprises providing a substantially vertical elongate tubular containment zone ( 1 ) containing a charge of the particulate solid ( 5 ), the volume of the containment zone ( 1 ) being greater than the settled volume of the particulate solid ( 5 ). An upper retainer means ( 3 ) is mounted at the upper end of the containment zone ( 1 ), the upper retainer means ( 3 ) being permeable to the fluid but adapted to retain particulate solid ( 5 ) in the containment zone ( 1 ). A follower means ( 4 ) is movably mounted in the containment zone ( 1 ) beneath the charge of particulate solid ( 5 ) for movement upwardly from the lower end of the containment zone ( 1 ) upon upward flow of elastic fluid through the containment zone ( 1 ) at a rate beyond a threshold rate. In the process the elastic fluid is caused to flow upwardly through the containment zone ( 1 ) at a rate which is sufficient to cause particulate solid ( 5 ) to rise up towards the upper end of the containment zone and form a cushion of particulate solid ( 5 ) against the underside of the upper retainer means ( 3 ). This rate is in excess of the threshold rate so as to cause the follower means ( 4 ) to move upwardly until it abuts against the underside of the cushion of particulate solid ( 5 ). The invention also provides an apparatus suitable for carrying out such a process and a method of loading a particulate solid into a substantially vertical tube.

1. TECHNICAL FIELD OF THE INVENTION

This invention relates to a process for contacting an elastic fluid witha particulate solid.

2. BACKGROUND OF THE INVENTION

There are many processes which involve contact between an elastic fluid,such as a gas or vapour, and a particulate solid. Thus many chemicalprocesses are carried out using gas phase or vapour phase reactionconditions in which a gas or vapour stream is contacted with aparticulate catalyst. Other processes in which an elastic fluid iscontacted with a particulate solid include drying, in which a gas orvapour is contacted with a desiccant, and adsorption, in which a gas orvapour is contacted with an absorbent for the purpose of, for example,adsorption of potential catalyst poisons therefrom.

In such processes the particulate catalyst or other particulate solid isfrequently in the form of a fixed bed, although some processes areoperated using a fluidised catalyst bed.

The conditions used in such processes often include high operatingtemperatures and/or high pressures. Hence reactors may have to withstandhigh thermal and pressure stresses. Typical constructional materials forchemical process vessels accordingly include mild steel, high pressuresteel, stainless steel and other special steels and alloys.

The use of catalysts, supported catalysts and other particulates, suchas desiccants and adsorbents, in fixed bed applications is thuswidespread. The particulate matter forming the fixed bed is typicallyceramic in nature or formed from pelletised metal oxides. Usually it hasa lower coefficient of expansion than the reactor, tube or othercontainment device for the particulate solid which is often composed ofmetal for pressure strength reasons. Thus, when the system increases intemperature, the particulate material slumps in the reactor because,upon heating, the walls of the reactor expand more than do the catalystparticles. Then when the temperature is later lowered, the walls of thereactor contract as it cools and the particulate matter may be caught asif by a tightening corset and thereby subjected to a crushing force,particularly if the particulate solid is contained in a substantiallyvertical metal tube.

In many applications the temperature variations in operation are notvery high and the different amounts of expansion between the particulatematter and the containment device are not significant. Consequentlyexcessive attrition of the particulate material or damage to containerwalls is not caused. However, in so-called fired processes which utilizehigh temperature operations, typically involving combustion in order tomaintain the temperature in endothermic catalytic processes such assteam reforming, or in exothermic catalytic processes such as partialoxidation processes, the amounts of expansion involved are considerable.If the fixed bed is contained in a large diameter reactor or containmentdevice, this differential expansion can be accommodated with only minorattrition of the catalyst particles since there are many particles andcumulative small movements of the catalyst particles into internalvoidage will occur. However, if the catalyst particles are contained ina narrow vertical tube having, for example, a nominal diameter of lessthan about 6 inches (about 15.24 cm), this relative movement isinsufficient and very high crushing forces can be generated. This tendsto result in attrition of the particulate matter, if friable to anydegree, or in damage to the tube wall, if not. The latter phenomenon hasbeen observed with physically strong alumina catalyst support balls inhigh temperature reformer tubes. Furthermore, in cases where thevertical tubes are very long and experience considerable expansion overtheir length due to the high operating temperature being used, forexample steam reformer tubes, the particulate matter drops by a verysignificant amount but cannot rise back up the tube when it cools due tobeing tightly squeezed by the cooling tube, a factor that exacerbatesthe crushing tendency.

Repeated heating and cooling cycles lead to a deterioration in thedesired characteristics of the packed bed, in that the originally loadedvolume of particulates is compressed to a higher density, therebyincreasing the pressure drop. In addition it has been found thatincreased pressure drop through a catalyst bed can be caused by, amongstother reasons, breakage of catalyst particles resulting from incorrectcharging of the catalyst or from differential expansion and contractionbetween the catalyst and the containing vessel due to temperaturecycling at start-up and shut-down. The breakage of catalyst particlesgives fragments of a smaller particle diameter, while erosion of thecorners of particles gives a lower voidage due to the eroded particlespacking more closely together. For further discussion reference may bemade to “Catalyst Handbook”, 2nd Edition, by Martyn V. Twigg (WolfePublishing Ltd., 1989), at page 125. This increased pressure dropgenerally increases the costs associated with gas compression in allfixed bed applications. In parallel fixed bed applications this can leadto increasing maldistribution, especially in a multi-tubular reactor,thereby causing different conversions and selectivities in differenttubes. This, in turn, can lead to further problems such as carbonlaydown, formation of hot spots (leading to possible tube failure and/orto sintering of the catalyst), and to development of different rates ofcatalyst deactivation which can further exacerbate the situation. Lossof catalyst surface material by spalling and attrition is particularlyserious when the active part of the catalyst is in the form of a shallowsurface layer, because in this case considerable catalyst activity canbe lost or the catalyst activity can become maldistributed.

The debris from the crushing forces will accumulate in the, by now, moredense bed and also increase the pressure drop. There will be anincreased likelihood of different pressure drops between different tubesin a multi-tubular reactor leading to maldistribution of the gas orvapour. In addition, the position of the top of the bed within anyindividual tube will be difficult to predict.

Another problem occurs with externally fired tubular reactors, such asreformers, in that any part of the tube that does not contain catalystis liable to overheat, with a consequent danger of tube failure, sincethere is no endothermic reaction being catalysed in that part of thetube to absorb the radiant heat and hence to cool that part of the tube.This makes it important to determine as closely as possible the positionof the catalyst bed during operation so as to minimize the risk of tubefailure through local overheating.

There is, therefore, a need in the art to provide a reactor design whichovercomes the problems associated with crushing of particulate materialswhen the reactor is subjected to temperature cycles of heating to hightemperatures followed by cooling again, and which allows low pressuredrop through the particulate material, minimizes pressure drop build-up,and allows the position of the bed to be fixed with a high degree ofcertainty so as to minimize the risk of tube failure in an externallyfired reactor.

This need has been recognized previously and there are various examplesin the prior art of attempts to overcome the problems outlined above.

The crushing of catalysts by radial forces due to wide temperaturecycles in tubular reactors, such as steam reforming reactors, has beenrecognized in U.S. Pat. No. 4,203,950 (Sederquist). In this document itis proposed that the catalyst should be arranged in an annulus with atleast one wall being flexible.

In U.S. Pat. No. 5,718,881 (Sederquist et al.) a steam reformer hassegmented reaction zones with individual supports for differenttemperature zones, the volume of the segments of catalyst beinginversely proportional to the temperature of the various zones in thereformer.

The use of flexible louvered screens to accommodate particle movement isproposed in U.S. Pat. No. 3,818,667 (Wagner). Louvers are also proposedin a catalytic converter for catalytically treating the exhaust gasesfrom an internal combustion engine in U.S. Pat. No. 4,063,900 (Mita etal.), and in U.S. Pat. No. 4,052,166 (Mita et al.).

It is proposed in U.S. Pat. No. 3,838,977 (Warren) to use springs orbellows in a catalytic muffler to control bed expansion and contractionso as to maintain a compacted non-fluidised or lifted bed. Springloading to maintain a bed of carbon granules tightly packed within afuel vapour storage canister housing is described in U.S. Pat. No.5,098,453 (Turner et al.).

A ratchet device to follow the decrease in volume of a bed but restrainback-movement of an upper perforated retaining plate is proposed in U.S.Pat. No. 3,628,314 (McCarthy et al.). Similar devices are described inU.S. Pat. No. 4,489,549 (Kasabian), in U.S. Pat. No. 4,505,105 (Ness),and in U.S. Pat. No. 4,554,784 (Weigand et al.).

Pneumatic sleeves inside a catalyst bed to restrain movement of theparticulate material are proposed in U.S. Pat. No. 5,118,331 (Garrett etal.), in U.S. Pat. No. 4,997,465 (Stanford), in U.S. Pat. No. 4,029,486(Frantz), and in U.S. Pat. No. 4,336,042 (Frantz et al.).

However, these prior art proposals are elaborate and do not solvesatisfactorily the problem of crushing of particulate catalysts whichcan be caused by repeated temperature cycling of a reactor tube.

Catalysts are usually passed over a screen to remove dust and brokenpieces either before shipment and/or before loading into a reactor. Suchremoval of dust and broken pieces of catalyst is desirable in order tominimize the pressure drop across the reactor caused by the catalystbed. This screening step constitutes a costly procedure both in terms offinance and time. Once loaded, catalyst particles usually cannot bere-arranged and the packed density only tends to increase.

The loading of catalysts can be achieved by a number of methods toreduce breakage and damage caused by free fall loading. For example,“sock” loading can be used in which the catalyst is put into long“socks”, usually made of fabric, which are folded or closed at one endwith a releasable closure or tie which can be pulled to release catalystwhen the sock is in position. Another method, which is more suitable foruse in forming beds in vessels of large diameter, for example from about0.75 m to about 4 m or more in diameter, than for loading tubes ofdiameter less than about 25 cm, is so-called “dense” loading in whichthe catalyst is fed through a spinning distributor so as to lay downconsecutive level layers rather than mounds of dumped catalyst. A thirdmethod, which is suitable for loading vertical tubes, utilizes wiredevices or wires in tubes which reduce falling velocities. One option isto utilize one or more spirals of wire inside the tube so that thecatalyst particles bounce their way down the tube and do not undergofree fall over the full height of the tube. As the tube is filled, sothe wire or wires is or are withdrawn upwardly, optionally with verticalfluctuations. Such devices are proposed, for example, in U.S. Pat. No.4,077,530 (Fukusen et al.).

A further possibility is to use a line having spaced along its length aseries of brush-like members or other damper members and to withdraw theline upwardly as the catalyst particles are fed into the tube, asdescribed in U.S. Pat. No. 5,247,970 (Ryntveit et al.).

“Sock” loading can also be carried out semi-continuously in largediameter vessels with a funnel and a filled fabric or solid tube whichis moved and raised to release the catalyst with frequent leveling ofthe catalyst.

Each method of loading produces fixed beds with different bulkdensities. The density differences can be quite marked; for example,with cylindrical particulate materials or extrudates the “dense” loadeddensity can be as much as about 18% greater than the corresponding“sock” loaded density due to the particles being laid generallyhorizontally and parallel to each other in the “dense” method ratherthan at random following “sock” removal.

In some applications it is desirable to maximize the amount of catalystloaded, despite increased pressure drop through the fixed bed, in whichcase “dense” loading or loading into liquid may be used and/or the tubesmay be vibrated.

U.S. Pat. No. 5,892,108 (Shiotani et al.) proposes a method for packinga catalyst for use in gas phase catalytic oxidation of propylene,iso-butylene, t-butyl alcohol or methyl t-butyl ether with molecularoxygen to synthesise an unsaturated aldehyde and an unsaturatedcarboxylic acid in which metal Raschig rings are used as auxiliarypacking material.

In U.S. Pat. No. 5,877,331 (Mummey et al.) there is described the use ofa purge gas to remove fines from a catalytic reactor for the productionof maleic anhydride which contains catalyst bodies. In this procedurethe purging gas, such as air, is passed through the catalyst bed at alinear flow velocity sufficient to fluidise the catalyst fines butinsufficient to fluidise the catalyst bodies. At column 15 lines 16 to18 it is said:

-   -   “In order to prevent fluidization or expansion of the catalyst        bed during further operation of the reactors, and in particular        to prevent the catalyst bodies in the fixed catalyst bed from        abrading against one another or against the tube walls, a        restraining bed comprising discrete bodies of a material        substantially denser than the catalyst was placed on top of the        column of catalyst in each tube of the reactors.”        It is also taught that this upflow removes undesirable fine        particles which, if left in the densely packed vessel, may        contribute to plugging of the bed.

In U.S. Pat. No. 4,051,019 (Johnson) there is taught a method forloading finely divided particulate matter into a vessel for the purposeof increasing the packing density by introducing a fluid mediumcounter-current to the downward flow of the finely divided particulatematter at a velocity selected to maximize the apparent bulk density ofthe particulate matter in the vessel. It is taught that this method alsoprovides a method of removing undesirable fine particles which, if leftin the densely packed vessel, might contribute to plugging of the bed.

Vibrating tubes with air or electrically driven vibrators and/orstriking with leather-faced hammers is described in the afore-mentionedreference book by Twigg at page 569, the latter being used to furthercompact the catalyst in those tubes showing low pressure drop inmulti-tube applications, in order to achieve equal pressure drops ineach tube.

An upflow tubular steam reformer is described in U.S. Pat. No. 3,990,858(O'Sullivan et al.). In this proposal fluidisation of the particulatematerial in the catalyst tubes is prevented by providing a weightedconically shaped hollow member which rests on top of the bed ofparticulate material. This conically shaped hollow member is providedwith elongated slots whereby fluid exiting from the bed flows into theinterior of the hollow member, through the slots and into the tubeoutlet.

There is a need to obviate in a simple and reliable way the problemscaused by crushing or attrition of particulate materials, such ascatalysts, desiccants or adsorbents, which are subjected to cyclingbetween high and low temperatures in vessels, particularly vessels madeof relatively high thermal expansion materials, such as steel or othermetals or alloys. There is also a need to provide a method of operatinga catalytic reactor in which the pressure drop across a catalyst bed canbe reliably minimized in operation. In addition there exists a need fora method of loading a tubular reactor with a particulate material, e.g.a particulate catalyst, in which the presence of “fines” can besubstantially avoided in the catalyst tube. Furthermore there exists aneed for a method of operating a reactor containing a charge of aparticulate material in which any “fines” which may be formed during thecourse of extended operation of the reactor can be removed simply fromthe reactor without having to discharge the charge of particulate solidfrom the reactor. There is also a need for operating a tubular reactorin which the position of the top of the bed of catalyst or otherparticulate material in the or each tube is known with certainty.

3. SUMMARY OF THE INVENTION

The present invention accordingly seeks to provide a novel process foreffecting contact between an elastic fluid, such as a gas or vapour, anda particulate solid under conditions which include use of cyclingbetween elevated temperatures and ambient or near ambient temperaturebut under which crushing of the solid particles is minimized. It furtherseeks to provide an improved process in which a gas or vapour iscontacted with a particulate solid, such as a catalyst, desiccant oradsorbent, which is subjected to elevated temperatures of severalhundreds of degrees Centigrade and then cooled without subjecting theparticulate solid to undue mechanical stresses. In addition, the presentinvention seeks to provide a process for contacting a gas or vapour witha particulate solid in a tube at elevated temperatures under conditionswhich minimize imposition of crushing forces on the solid, particularlyduring cooling of the tube, and which facilitate removal of fragments ofthe particulate solid formed by attrition of the particles of catalystor other solid so as substantially to obviate any significant increaseof pressure drop. Furthermore the invention seeks to provide a new andimproved method of packing a catalyst bed. Yet another objective of thepresent invention is to provide a method of operating a catalyticreactor tube packed with catalyst particles wherein the position of thetop of the catalyst bed is known with certainty despite the use ofelevated temperatures which cause the reactor tube to expand bothlongitudinally and radially. The invention further seeks to provide amethod of operating a catalytic reactor, more particularly a tubularreactor in which a gaseous or vaporous phase is contacted with aparticulate catalyst, so that the pressure drop across the catalyst bedis minimized. It also seeks to provide a method of loading a tubularreactor with a particulate material, such as a particulate catalyst, inwhich the production of undersized “fines” particles is substantiallyobviated and in which any such “fines” particles can be removed from thecatalyst bed without first discharging the catalyst from the reactor.

According to one aspect of the present invention there is provided aprocess in which an elastic fluid is contacted with a particulate solid,which process comprises the steps of:

-   -   (a) providing a substantially vertical elongate tubular        containment zone containing a charge of the particulate solid,        the volume of the containment zone being greater than the        settled volume of the charge of particulate solid;    -   (b) providing upper retainer means mounted at the upper end of        the containment zone, the upper retainer means being permeable        to the fluid but adapted to retain particulate solid in the        containment zone, and follower means movably mounted in the        containment zone beneath the charge of particulate solid for        movement upwardly from the lower end of the containment zone        upon upward flow of elastic fluid through the containment zone        at a rate beyond a threshold rate; and    -   (c) causing the elastic fluid to flow upwardly through the        containment zone at a rate which is sufficient to cause        particulate solid to rise up towards the upper end of the        containment zone and form a cushion of particulate solid against        the underside of the upper retainer means and which is in excess        of the threshold rate so as to cause the follower means to move        upwardly until it abuts against the underside of the cushion of        particulate solid.

The invention further provides an apparatus for effecting contact of anelastic fluid with a particulate solid comprising:

-   -   (a) reactor means defining a substantially vertical elongate        tubular containment zone for containing a charge of the        particulate solid, the volume of the containment zone being        greater than the settled volume of the charge of the particulate        solid;    -   (b) upper retainer means mounted at the upper end of the        containment zone, the upper retainer means being permeable to        the fluid but adapted to retain particulate solid in the        containment zone; and    -   (c) follower means movably mounted in the containment zone        beneath the charge of particulate solid for movement upwardly        from the lower end of the containment zone upon upward flow of        elastic fluid through the containment zone at a rate beyond a        threshold rate;

whereby upon causing the elastic fluid to flow upwardly through thecontainment zone at a rate which is sufficient to cause particulatesolid to rise up towards the upper end of the containment zone and forma cushion of particulate solid against the underside of the upperretainer means and which is in excess of the threshold rate the followermeans moves upwardly until it abuts against the underside of the cushionof particulate solid.

The elastic fluid may comprise a gaseous or vaporous medium.

The upper retainer means is permeable to the elastic fluid but adaptedto retain undamaged particles of the particular solid in the containmentzone. It may comprise a screen of substantially parallel bars, rods orwires, or a wire mesh or other perforate form of retainer, such as aplate formed with numerous apertures.

The follower means is desirably designed so that there is a gap or gapsthrough and/or around it for upward flow of elastic fluid therethrough.Moreover the lower end of the containment zone is desirably designed sothat, when there is no upward flow of elastic fluid through thecontainment zone, yet there is a gap or gaps for elastic fluid to flowupwardly through or around the follower means when such upward flowcommences but remains below the threshold rate. Thus the follower meanstypically includes a piston portion which is a loose fit in thecontainment zone so that fluid can pass up through an annular gapsurrounding the piston portion. This piston portion can be disposed ator towards the lower end of the follower means, at or towards the upperend of the follower means, or intermediate the upper and lower ends ofthe follower means. One of the functions of the follower means is tosupport the charge of particulate solid when any upward flow of fluid isinsufficient to cause particulate solid to rise upwardly in thecontainment zone to form a cushion against the underside of the upperretainer means. If the piston portion is at or near the upper end of thefollower means, then the piston portion can perform this function; ifnot, then the follower means preferably includes, at or towards itsupper end, support means for supporting the charge of particulate solidwhen any upward flow of fluid is insufficient to cause particulate solidto rise upwardly in the containment zone to form a cushion ofparticulate solid against the underside of the upper retainer means, forexample a series of concentric rings spaced one from another so that thegaps between adjacent pairs of rings are insufficient to allow aparticle of predetermined size of the particulate solid to passtherethrough. Such gaps also assist in distributing the flow ofupflowing elastic fluid more uniformly across the cross-section of thecontainment zone.

Instead of using concentric rings it is alternatively possible to use amesh arrangement to provide support for the charge of particulate solidwhen any upward flow of elastic fluid is insufficient to causeparticulate solid to rise upwardly in the containment zone to form acushion of particulate solid against the underside of the upper retainermeans.

The follower means should further be designed so that, despite theannular gap around the piston portion, the follower means cannot tiltsufficiently from a vertical position to become jammed against the wallsof the containment zone. In one design this is achieved by providing thepiston portion with a series of substantially vertical plates radiatingfrom a vertical axis, for example three vertical plates in a Y-sectionarrangement, the plates being arranged vertically with their planes atangles of approximately 120° to one another around a substantiallyvertical axis of course more than three plates can be used, if desired,for example four plates arranged vertically in an x-section at 90

to one another around a substantially vertical axis.

Alternatively, the piston portion can be provided with a centralvertical rod with one or more spider sets formed by three or more rodsor bars radiating from the central vertical rod, for example threeradiating rods set at an angle of approximately 120° to one another andpositioned so as to prevent the follower means from tilting asignificant amount as it moves within the containment zone and hencefrom jamming against the walls of the containment zone. In this way thefollower means can allow elastic fluid to pass freely at all timesaround it in either the upward or downward direction, while ensuringthat, as the rate of upward flow of elastic fluid is increased to a ratebeyond the threshold rate, the follower means lifts smoothly off fromits position at the bottom end of the containment zone and then moves upthe containment zone until it abuts against the underside of the cushionof particulate solid.

When the elastic fluid flows upwardly at a low flow rate through thecontainment zone, the follower means remains at the lower end of thecontainment zone with the particulate solid supported on it in the formof a bed. As the upward flow rate increases, the particles of theparticulate solid become fluidised at the upper end of the bed. Uponstill further increase of the upward flow rate, the proportion of thebed that is fluidised increases until particles begin to rise up thecontainment zone and form a cushion of particles against the undersideof the upper retainer means. When the upward flow rate is sufficient forsubstantially all of the particles to have lifted, some of the particleson the lower side of the cushion of particles tend to fall off and thenbe carried up again. At an upward flow rate beyond the threshold flowrate, the follower means is lifted and comes to abut against theunderside of the cushion of particles thereby holding the cushion ofparticles in place and preventing particles from falling off the cushionof particles while the follower means remains in place against theunderside of the cushion of particles.

The elongate containment zone may be one of a plurality of elongatecontainment zones connected in parallel, for example it may be acatalyst tube 1 mounted in the furnace 40 of a steam reformer (FIG. 7).

Preferably at least part of the containment zone is of substantiallyuniform horizontal cross-section. More preferably the containment zoneis of substantially uniform horizontal cross-section throughout at leasta major part of its height and even more preferably throughoutsubstantially all of its height.

The follower means is adapted to rise upwardly up the containment zonewhen the upward flow rate of elastic fluid is greater than the thresholdflow rate until it abuts against the cushion of particulate solid. Thusat least that part of the containment zone in which the follower meansmoves should desirably be of uniform horizontal cross section. Forexample it may comprise a tube of substantially circular cross section.

In a preferred embodiment the containment zone comprises a tube whichhas a length:diameter ratio of from about 50:1 to about 1000:1, morepreferably from about 100:1 to about 750:1. Normally such a tube has aninternal diameter of about 6 inches (about 15.2 cm) or less, preferablyan internal diameter of about 2 inches (about 5.08 cm) or less, e.g. atube having an internal diameter of from about 1 inch (about 2.54 cm) toabout 2 inches (about 5.08 cm).

In many cases it is possible to design the containment zone so that thedistance through which the follower means rises up the containment zonein operation is at most only a few inches, for example from about 1 inch(about 2.54 cm) up to about 10 inches (about 25.40 cm), preferably fromabout 2 inches (about 5.08 cm) to about 5 inches (about 12.70 cm), e.g.about 3 inches (about 7.62 cm).

Although it will frequently be preferred for the containment zone to beof substantially uniform cross-section throughout its height, it isalternatively possible for a lower portion of the containment zone inwhich the follower means moves in operation to have a smaller area ofcross-section than an upper part of the containment zone. Hence thecontainment zone can comprise a lower tubular portion of relativelysmall diameter attached to the bottom of a tube of larger diameter. Inthis case, while the narrower lower portion of the containment zone inwhich the follower means moves in operation requires to be machined to arelatively close tolerance, the transverse dimensions of the upperportion of the containment zone do not have to be so carefullycontrolled. A further advantage in such an arrangement is that the gapbetween the follower means and the walls of the lower portion of thecontainment zone can be larger than if the follower means is arranged toslide in a larger tube. Again this factor reduces the need for carefulmachining of the inside of that part of the containment zone in whichthe follower means moves.

It will usually be preferred that the follower means is arranged toblock passage of elastic fluid up or down the containment zone butpermit upward passage of elastic fluid through a clearance gap betweenthe internal surface of the containment zone and the follower means, theclearance gap providing a clearance less than the smallest dimension ofa non-fragmented particle of the particulate solid. Hence the followermeans may comprise a closed lower end portion for defining the clearancegap and an upper portion provided with elastic fluid passing means. Suchelastic fluid passing means may comprise a plurality of substantiallyconcentric rings spaced one from another, the clearance between adjacentrings being less than the smallest dimension of a non-fragmentedparticle of the particulate solid. Alternatively the elastic fluidpassing means may comprise a perforate baffle member whose perforationsare smaller the smallest dimension of a non-fragmented particle of theparticulate solid.

The containment zone may contain a plurality of types of particulatesolid, in which case each type can be separated from an adjacent type bymeans of a respective follower means (FIG. 8).

Typically the particulate solid has at least one dimension less thanabout 10 mm, e.g. about 6 mm. The particulate solid may be substantiallyspherical in shape and have, for example, a diameter of from about 2 mmto about 10 mm, e.g. about 6 mm. However, other shapes of particulatesolid can alternatively be used but the use of shapes which can easilyform bridges should be avoided. Thus other shapes which can be usedinclude rings, saddles, pellets, cylindrical extrudates, trilobates,quadrilobates, or the like.

Examples of suitable particulate solids include catalysts, desiccantsand adsorbents.

One method of loading the particulate solid into the containment zoneinvolves loading via the top of the containment zone against a gentleupflow stream of elastic fluid at a rate less than that required to liftfully any already charged particulate solid (or to move the followermeans upwardly) but such that the particulate solid does not fall freelyunder gravity. In this way the danger of damage to the particulate solidcan be significantly reduced or substantially eliminated.

Any other method of loading, e.g. “sock” loading, can, however, be used.Other techniques that can be used include the use of wire devices, theuse of devices as described in U.S. Pat. No. 5,247,970 (Ryntveit etal.), or the like.

After initial loading of the particulate solid and optionally mountingin position the upper retainer means, the pressure drop across thecontainment zone can be measured in upflow or downflow mode, whereupon,after applying an upflow stream of elastic fluid to the particulatesolid with the upper retainer means in position, the settled volume ofparticulate solid in the containment zone and/or the pressure dropacross the containment zone can be checked, particulate solid beingadded to, or removed from, the containment zone if the settled volume ofparticulate solid in the containment zone does not correspond to apredetermined value and/or if the pressure drop across the containmentzone is not within the desired range. Hence in a preferred procedure,after initial loading of the particulate solid, the pressure drop acrossthe containment zone is measured in a measurement step. Then particulatesolid can be added to or removed from the containment zone if thepressure drop measured does not conform to a predetermined value.Alternatively, or in addition, after initial loading of the particulatesolid the settled volume of particulate solid in the containment zonecan be measured in a measurement step, whereafter particulate solid maybe added to or removed from the containment zone if the settled volumeof particulate solid in the containment zone does not conform to apredetermined value. In either case, after initial loading of theparticulate solid but prior to the measurement step, elastic fluid canbe caused to flow upwardly through the containment zone at a rate inexcess of the threshold rate so as to cause the particulate solid toform a cushion of particulate solid against the underside of the upperretainer and so as to cause the follower means to rise up thecontainment zone until it abuts against the underside of the cushion ofparticulate solid, thereafter the upward flow of elastic fluid beingreduced or discontinued so as to permit formation of a settled bed ofparticulate solid.

In one particularly preferred process according to the invention theparticulate solid is a catalyst effective for catalysing a desiredchemical reaction, e.g. steam reforming, and an elastic fluid comprisinga reaction feed mixture capable of undergoing the desired chemicalreaction is passed in upflow mode through the containment zone while thecontainment zone is maintained under operating conditions effective forcarrying out the desired chemical reaction. In an alternative processaccording to the invention the particulate solid is a catalyst effectivefor catalysing a desired chemical reaction, and an elastic fluidcomprising a reaction feed mixture capable of undergoing the desiredchemical reaction is passed in downflow mode through the containmentzone while the containment zone is maintained under operating conditionseffective for carrying out the desired chemical reaction.

In the process of the invention the containment zone and the particulatesolid can be subjected to an elevated temperature, for example atemperature of at least about 500° C. For example, the desired chemicalreaction may be a partial oxidation reaction, in which case the elasticfluid comprises a partial oxidation feed mixture, the particulate solidis a partial oxidation catalyst, and the temperature of the containmentzone and the partial oxidation catalyst is maintained by the partialoxidation reaction. Alternatively the desired chemical reaction may be asteam reforming reaction, in which case the elastic fluid comprises asteam reforming feed mixture, the particulate solid is a steam reformingcatalyst, and the temperature of the containment zone and the steamreforming catalyst is maintained by hot combustion gases external to thecontainment zone.

The invention further provides a method of loading a particulate solidinto a substantially vertical tube in readiness for conducting a methodin which an elastic fluid is contacted with the particulate solid, whichmethod comprises the steps of:

-   -   (a) providing a substantially vertical elongate tubular reactor        having an elongate containment zone for containing a charge of a        particulate solid;    -   (b) providing at the lower end of the containment zone follower        means movably mounted in the containment zone for movement        upwardly from the lower end of the containment zone upon upward        flow of elastic fluid through the containment zone at a rate        beyond a threshold rate;    -   (c) loading a predetermined charge of the particulate solid into        the containment zone on top of the follower means, the settled        volume of the particulate solid being less than the volume of        the containment zone;    -   (d) mounting at the upper end of the containment zone upper        retainer means permeable to the fluid but adapted to retain        particulate solid in the containment zone; and    -   (e) causing an elastic fluid to flow upwardly through the        containment zone at a rate which is sufficient to cause        particulate solid to rise up towards the upper end of the        containment zone and form a cushion of particulate solid against        the underside of the upper retainer means and which is in excess        of the threshold rate so as to cause the follower means to move        upwardly until it abuts against the underside of the cushion of        particulate solid. In such a method said particulate solid may        be loaded via the top of said containment zone against an upflow        stream of elastic fluid at a rate less than that required to        lift fully said particulate solid but such that said particulate        solid does not fall freely under gravity. Preferably, after        applying an upflow stream of elastic fluid to said particulate        solid, the settled volume of particulate solid in the        containment zone is checked. Particulate solid can be added to        or removed from the containment zone if the settled volume of        particulate solid in the containment zone does not conform to a        predetermined value.

In a particularly preferred loading method the upward flow of elasticfluid is maintained in step (e) for a period and at a rate sufficient tocause substantially all particles which are smaller than a predetermineddesign particle size and are sufficiently small to pass through theupper retainer means to pass through the upper retainer means.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a semi-diagrammatic side view of a vertical reactor tubehaving a catalyst follower therein with no upward gas flow;

FIG. 2 is a side view of the vertical reactor tube of FIG. 1 with anupward gas flow at a rate in excess of a threshold gas flow rate;

FIG. 3 is a side view of the catalyst follower of FIGS. 1 and 2 on anenlarged scale;

FIG. 4 is a top plan view of the catalyst follower of FIG. 3;

FIG. 5 is a perspective view from above of an alternative catalystfollower; and

FIG. 6 is a perspective view from below of the catalyst follower of FIG.5.

FIG. 7 depicts a plurality of elongate containment zones connected inparallel.

FIG. 8 depicts separation of a plurality of types of particulate solidsby respective follower means.

5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, there is shown a vertical reactortube 1 for carrying out a gas phase or vapour phase reaction, such as asteam reforming process. This process can be operated in upflow ordownflow mode, as desired. However, for reasons which will be furtherexplained below, upflow mode is preferred in the practice of the presentinvention.

Tube 1 is circular in cross section and has an internal diameter ofabout 2 inches (about 5.08 cm) and is provided with an internal annularledge 2, or with a removable support with a central vertical aperture,and with an upper perforate retainer 3. It can be made of any suitablematerial that is substantially inert under the reaction conditions to beused. For, example, it can be a stainless steel or alloy tube or a mildsteel tube, depending upon the nature of the reaction to be carried outand the reaction pressure.

Although reactor tube 1 for convenience usually has a circular crosssection, tubes of other cross sections, such as elliptical, hexagonal,or square cross section may be used, if desired.

The length of reactor tube 1 is a multiple (which can be either a wholenumber multiple, e.g. 100×, or a fractional number multiple, e.g.37.954×) of the diameter or other transverse dimension of the reactortube 1. Although reactor tube 1 as illustrated is relatively short, itwill be appreciated by those skilled in the art that reactor tube 1 canbe of any convenient length. For example, reactor tube 1 can be about 6feet (about 182.88 cm) long or more, e.g. up to about 30 feet (about914.40 cm) or 45 feet (about 1371.60 cm) or more, if desired.

When there is no upward flow of gas or vapour, ledge 2 supports acatalyst follower 4 on top of which is disposed a charge 5 of aparticulate catalyst. The settled volume of the charge 5 of particulatecatalyst, whether this is densely packed or loosely packed, is less thanthe available volume between the top of the catalyst follower 4 and theupper perforate retainer 3.

The catalyst particles may be of any desired size or shape but aretypically substantially spherical. Typically the catalyst particles haveno dimension which is smaller than about 3 mm. They may be substantiallyspherical particles which have, for example, a diameter of about 6 mm.However, the particles may have any other desired shape, for example,cylinders (optionally with one or more passages formed therein),cylindrical extrudates, or trilobe or quadrilobe extrudates, so long asthe shape of the particles is not conducive to the formation of bridges.The catalyst particles are sufficiently large not to pass through anyannular gap between catalyst follower 4 and the internal wall of reactortube 1 nor to pass through upper perforate retainer 3.

The upper perforate retainer 3 is intended to prevent passage ofundamaged catalyst particles upwardly beyond upper perforate retainer 3.It will, however, allow dust or small fragments of abraded catalyst topass upwardly therethrough. It may consist of or include a wire gauze ormesh of appropriate mesh size.

Catalyst follower 4 is made from a suitable material, such as stainlesssteel, and comprises three plates 6 welded together axially andsymmetrically so as to form a Y-section central portion with the plates6 set at 120° to one another about a vertical axis. The radially outeredges of plates 6 are closely spaced from the internal wall of reactortube 1 and help to maintain catalyst follower 4 in an upright positionand guide it in its movement up and down the reactor tube 1 as furtherdescribed below.

As can be seen from FIGS. 1 and 2, and more clearly from FIG. 3, theupper part 7 of each plate has a stepped profile and annular rings 8, 9,10, and 11 are welded to this stepped profile. The clearance between theannular rings 8, 9, 10, and 11 is less than the average smallestdimension of the catalyst particles and the lateral dimensions of therings are so chosen that the catalyst particles cannot drop down throughcatalyst follower 4 but are retained on the upper side thereof. Near thelower end of catalyst follower 4 the plates 6 are welded to a disc 12below which there are also welded lower plates 13.

There is an annular gap 14 around disc 12 to allow upward passage of gasor vapour. In addition there is a central aperture 15 at the top end ofcatalyst follower 4, as can be seen in FIG. 4. However, when gas orvapour passes up reactor tube 1 at a flow rate in excess of a thresholdflow rate, disc 12 acts as a loose piston and so catalyst follower 4rises in reactor tube 1. The weight of the catalyst follower 4 is soselected, and the size and shape of the catalyst follower 4 are sochosen, that the upward lifting forces due to the upflowing gas orvapour at such a flow rate cause catalyst follower 4 to float up thetube 1 thereby sweeping any non-fluidised particulate material before itand compressing the cushion of particles 5 against the fixed upperperforate retainer 3.

It will be seen that catalyst follower 4 includes a lower spacer sectionconstituted by plates 13 which serves to hold the piston part formed bydisc 12 away from the ledge 2 mounted in tube 1 when there is no upflowof elastic fluid and when catalyst follower 4 is supported on ledge 2.This results in gas or vapour being able, at all times, to pass freelyin upflow or in downflow past this piston part. Disc 12 allows smoothlift of the catalyst follower 4 in upflow operation. The weight ofcatalyst follower 4 is selected so that, at the desired operating upflowgas rate, the uplift force caused by the pressure loss across theannular gap 14 between the disc 12 and the inside wall of reactor tube 1is greater than the gravitational pull of the total mass of the catalystfollower 4.

FIG. 2 illustrates the reactor tube 1 when gas or vapour is flowing upthe reactor tube 1 at a flow rate in excess of a threshold flow rate.The catalyst particles have lifted to form a cushion of catalystparticles 5 abutting against the underside of upper perforate retainer3. In addition catalyst follower 4 has also lifted and is itselfpressing against the underside of the cushion of catalyst particles 5.

By varying the size of the portions cut out of the radially outer sidesof plates 6, it is possible to alter the weight of the catalyst follower4. It accordingly becomes possible to vary the threshold flow rate, i.e.the upward flow rate of gas or vapour within a given tube 1 at which thecatalyst follower 4 will lift from ledge 2.

If desired, concentric rings 8, 9, 10, and 11 can be replaced by a gauzeor lattice arrangement.

An alternative form of catalyst follower 24 is illustrated in FIGS. 5and 6. This is cast from a suitable alloy. This comprises a bottom disc25 below which are three spacer elements 26 that are set at 120° to oneanother and that serve to support catalyst follower 24 on the ledge 2when there is no upflow of gas through reactor tube 1. The gaps betweenspacer elements 26 and the annular gap around bottom disc 25 serve topermit gas to flow upwards around catalyst follower 24 at low gasvelocities and to permit catalysts follower 24 to lift off from ledge 2when the upward gas flow rate exceeds the threshold rate. Above disc 25is a rod portion 27 from whose upper end project three stepped flanges28, which are radially spaced one from another around the axis of therod portion 27 by an angle of 120°. Secured to flanges 28 are a seriesof rings 29, 30, 31 and 32, the spacing between adjacent rings beingless than the smallest dimension of an undamaged catalyst particle. Inthis way catalyst particles cannot pass down the tube below catalystfollower 24 whereas gas or other elastic fluid can pass up the tube atflow rates both below and above the threshold value at which catalystfollower 24 will lift off the ledge 2.

Instead of providing reactor tube 1 with an internal ledge 2, it isexpedient to replace the ledge 2 by a number of small inwardly directedprojections, for example, 3 or 4 small projections, the spaces betweenwhich provide a passage for upward flow of elastic fluid past bottomdisc 25. In this case plates 13 or spacer elements 26 would not berequired. Alternatively ledge 2 can be replaced by a removable supportdevice, which is formed with a central vertical aperture, so as toenable the reactor tube 1 to be emptied downwardly, if necessary.

The operation of a preferred process using the apparatus of FIGS. 1 to 4will now be described. The apparatus of FIGS. 5 and 6 can be used in asimilar way.

In order to load catalyst particles into tube 1 any suitable method canbe used. For example, if the catalyst is sufficiently robust, upperperforate retainer 3 can be removed and the catalyst then carefullypoured in until the desired amount has been introduced. Since reactortube 1 is of relatively small cross section, the catalyst particles tendto collide with the walls of the tube and thus do not ever undergoabsolutely free fall. Hence their passage down the reactor tube 1results in their rattling their way down the tube 1 rather thanundergoing free fall. If the catalyst is of a frangible nature, then anyof the previously mentioned techniques using wires, wire coils, or thedevices of U.S. Pat. No. 5,247,970 (Ryntveit et al.) can be used.Alternatively the “sock” technique can be used, for example.

After loading of the catalyst charge the settled volume of the catalystcan be measured and compared with a design value. If that settled volumeis greater than or less than the design value, then some of the catalystcan be removed or more catalyst can be loaded, as appropriate. Inaddition, before the desired process, e.g. steam reforming or partialoxidation, is brought on line, it will usually be desirable to installthe upper perforate retainer 3 and to pass a gas, such as nitrogen, upthe tube 1 at a rate in excess of the threshold rate so as to cause thecatalyst and the catalyst follower 4 to rise up the tube 1 and form acushion of catalyst particles immediately under the upper perforateretainer 3. This upflow can be maintained for a sufficient length oftime and at a rate to allow substantially all “fines” particles with aparticle size small enough to pass through the upper perforate retainer3 to pass therethrough and be swept away by the gas. This procedure canbe repeated as many times as necessary by reducing the gas flow untilthe catalyst follower 4 and catalyst fall back down the tube, and thenincreasing the flow of gas again past the threshold rate. Then thepressure drop across the catalyst charge, either in upflow through thecushion of catalyst or in downflow through the settled bed of catalystcan be measured and compared to a design value. If either the settledvolume or the pressure drop are not as desired, then the upper perforateretainer 3 can be removed to permit more catalyst to be added or some ofthe catalyst to be removed, as appropriate, and the procedure repeateduntil the measurements indicate that the loading of catalyst in tube 1is considered satisfactory.

If more than one type of catalyst is to be loaded into reactor tube 1,then a further catalyst follower 4 can be added after each type ofcatalyst has been loaded except after the final type of catalyst hasbeen loaded.

At low upflow rates the gas or vapour flows through the settled bed ofcatalyst particles. However, as the flow rate increases, so at leastsome of the catalyst particles will tend to lift, forming initially apartially fluidised bed above a lower static bed of catalyst particles.As the flow rate is increased, more and more of the catalyst particlesare fluidised and travel up the reactor tube 1 to form a cushion ofcatalyst particles against the underside of upper perforate retainer 3.Any dust or under-sized particles will tend to pass through the upperperforate retainer 3 during this procedure. Upon further increase offlow rate, substantially all of the catalyst particles are lifted fromon top of catalyst follower 4 into the cushion of catalyst particleswith a relatively small number of particles in motion just under thecushion of catalyst particles, these moving particles falling away fromthe cushion under gravity and then being carried back up again by theupflowing gas or vapour. Eventually, as the flow rate increases stillfurther, the catalyst follower 4 moves upwards until it abuts againstthe underside of the cushion of catalyst particles, as illustrated inFIG. 2, thereby preventing any further movement of the catalystparticles and thus possible attrition thereof.

During this procedure the upflowing elastic fluid may be an inert gas ora reactant gas required for pre-treatment of the catalyst. For example,in the case of a hydrogenation catalyst, the upflowing elastic fluidduring this phase of operation may be a hydrogen-containing gas requiredfor pre-reduction of the catalyst. Pre-treatment can be effected at anyappropriate temperature or pressure. Thus pre-treatment can be effectedat ambient temperature or at elevated temperature, as appropriate, andcan be effected at ambient pressure, at sub-ambient pressure, or atelevated pressure, as need be.

If reactor tube 1 is to be used in upflow mode, then following anynecessary pre-treatment of the catalyst particles in the cushion ofcatalyst particles, the flow of elastic fluid can be switched to thereactant gas or vapour mixture and any necessary adjustment of thetemperature or pressure carried out in order to allow an operatingcampaign to be carried out. For example, if the reactor tube 1 is a tubemounted in the furnace of a steam reformer, it may be heated to atemperature of 500° C. or more, for example to at least about 750° C. upto about 1050° C., and maintained under a pressure of, for example,about 100 psia to about 600 psia (about 698.48 kPa to about 4136.86kPa). In the course of being heated to the elevated operatingtemperature, the reactor tube 1 will expand radially and longitudinallyand the catalyst, having a lower expansion coefficient, will move tofill the increased space. However, the location of the top of thecushion of catalyst particles will be fixed at all times since theposition of the upper catalyst retainer 3 is known and remains fixed,while the bottom of the cushion will move upwards marginally. Thisfixing of the position of the top of the cushion of catalyst, i.e. thetop of the catalyst bed in operation, is of great advantage inmulti-tubular reactors, for example, where introduction of heat needs tobe precisely located relative to the catalyst, such as in the furnace ofa steam reformer, or where the level of a liquid coolant or heatingmedium outside the tubes needs to be located precisely relative to thecatalyst, such as in an exothermic reaction controlled by raising steamfrom a controlled level of boiling water, for example in Fischer-Tropschreactions, in hydrogenation reactions, or the like. In addition, it hasthe added benefit of substantially obviating the problem of tube failurethrough lack of control of the temperature within or outside a catalystfilled tube.

At the end of an operating campaign, the reactant feed can be switchedto an inert gas or to air, as appropriate, either before or afterallowing the pressure to return to standby or shutdown pressureconditions, while allowing the reactor tube 1 to cool. Alternatively, ifthe catalytic reaction is endothermic, the supply of heat to the outsideof the tubes can be reduced while maintaining a flow of precess fluidthrough the reactor tube 1 as it cools. Then the flow rate of elasticfluid can be reduced, thus allowing catalyst follower 4 and catalystparticles 5 to drop back in controlled fashion until catalyst follower 4again rests on ledge 2 (or on the removable support device, if ledge 2is replaced by a removable support device, as described above, so as toenable the reactor tube 1 to be cleared downwardly) and catalystparticles return gently to the condition illustrated in FIG. 1 withminimum damage to the catalyst.

On re-start in upflow mode, the catalyst will have been partiallyremixed. If reactor tube 1 is a tube of a multi-tubular reactor, thecatalyst particles will reform a consistent low packing density in allthe tubes, while fines and debris will be removed by the gas upflow.Hence the pressure drop across each tube will remain substantiallyconstant throughout the life of the catalyst.

During the cooling operation at the end of an operating campaign inupflow mode, the gas flow can be increased one or more times to recreatethe cushion of catalyst particles against the underside of upperperforate retainer 3, whereafter the gas flow can again be reduced inorder to prevent the formation, during cooling of the reactor tube 1, ofany “bridges” of catalyst particles, which could otherwise lead to adanger of crushing forces being exerted on the catalyst particles by thecontracting walls of the reactor tube 1 as it cools.

It is also possible to interrupt an upflow operating campaign byswitching the flow of elastic fluid to an inert gas, in the case of anexothermic catalytic reaction, or by reducing the rate of supply of heatto the outside of the reactor tube while maintaining a flow of processfluid through the reactor tube 1 in the case of an endothermic reaction,and then allowing the catalyst particles and catalyst follower 4 to dropby reducing the flow of inert gas or process fluid. The gas flow canthen be returned to a value which causes the cushion of catalystparticles to be re-formed. In the course of re-forming the cushion ofcatalyst particles, any dust or catalyst fragments will tend to passthrough the upper perforate retainer 3, thus removing a potential causeof undesired increase of pressure drop across the catalyst cushion.Thereafter the inert gas can be switched back to an upflowing reactantmixture, or the rate of heat supply can be increased, to continue theupflow operating campaign.

If reactor tube 1 is to be used in a downflow mode, then after thecushion of catalyst particles has been formed as shown in FIG. 2 and, ifdesired any necessary pre-treatment of the catalyst has been effected,the upflow of gas or vapour is reduced and then gradually stoppedthereby allowing the catalyst particles to settle out into a conditionsimilar to that shown in FIG. 1. In this condition the catalystparticles have a low packing density in the bed of catalyst particles.In downflow operation, as the reactor tube 1 reaches operatingtemperature, especially if that operating temperature is over 500° C.(for example, if reactor tube 1 is a tube in the furnace of a steamreformer), it will expand radially and longitudinally and the catalyst,having a lower expansion coefficient, will tend to slump and drop insidereactor tube 1. The location of the top of the catalyst bed at thispoint is not known with certainty. When the process is shut down, thecatalyst particles would normally be subjected to considerable crushingforces. To obviate this danger, an upflow of suitable optionallypreheated gas can be initiated at a rate sufficient to lift the catalystparticles within the tube 1 while the tube 1 and the catalyst cool. Thisminimizes crushing of the catalyst particles and re-orients the bed to alow packing density ready for re-start. A further advantage is that anyfines and debris are removed at each shut-down.

The reactor tube 1 may be, for example, a catalyst tube in the furnaceof a steam reformer. Since it is desirable to pack each catalyst tubewith catalyst in exactly the same manner so that the pressure dropacross each catalyst tube is substantially identical to thecorresponding pressure drop for every other catalyst tube of thereformer furnace, the catalyst tubes can be loaded in turn by thegeneral method described above. In this case an upflow of a gas, such asair, can be used in order to reduce the falling velocity of theparticulate catalyst material. This air flow can be applied solely tothe tube being loaded by plugging the upper ends of all other tubes andsupplying air to a common lower header space, or by applying air to thebottom of each tube in turn. The latter option is preferred becauseother operations can then be performed on the loaded tube while othertubes are being loaded.

The invention is further illustrated by means of the following Examples.

EXAMPLE 1

A glass tube 1, which was 2 meters long with an internal diameter of38.1 mm, was set up vertically with a follower 4 of the type illustratedin FIGS. 1 to 4 initially positioned at its bottom end. This follower 4had a disc 12 of diameter 36 mm. A charge of 1.84 kg of a nickelcatalyst (nickel on calcia-alumina support catalyst balls of nominaldiameter 6 mm) was dropped carefully into the tube. After loading, theupper perforate retainer 3 was fitted at a desired height in the tube 1.This retainer consisted of a Johnson wedge-wire screen comprising 1.5 mmwire with a 2 mm gap. The tube 1 was not filled fully to allow for thelower bulk density of the catalyst during the tests. Compressed air wasintroduced via a pressure regulator and flow rotameter (not shown) tothe bottom of the tube 1 at a rate at least sufficient to lift thecatalyst and the catalyst follower 4 such that a consolidated cushion ofcatalyst balls 5 was formed at the top of the tube 1 immediately underthe retainer 3. The height of the catalyst bed 5 was measured beforeintroducing air. The air flow was then reduced to allow the catalystfollower 4 to move back down to the bottom of tube 1 and also to allowthe catalyst balls to move back down to the bottom of the tube 1. Thisprocedure was repeated a number of times, from which data the followingaverage apparent bulk densities in kg/m³ were determined. The densitieswere found to be very repeatable, with the following small variationsover 360 tests during which the catalyst was removed and replaced after10, 20 and 120 tests:

After loading (free drop) 1157 +/− 1.0% (over four loadings) Lifted(with air flow) 1017 +/− 0.5% (within any one loading) Lifted (with airflow) 1017 +/− 1.5% (over all the tests) Dumped (with no air flow) 1000+/− 0.5% (within any one loading) Dumped (with no air flow) 1000 +/−1.0% (over all the tests)

EXAMPLE 2

The weight of catalyst used in Example 1 was checked after 10, 20, 120and 360 tests and showed 0.38% weight loss over 360 tests. In separatetests in the same apparatus the flow resistance of the fresh and worncatalyst particles used in Example 1 was compared. At an air flow rateof 49.14 Nm³/h the fresh catalyst particles exhibited a pressure drop of1.21×10⁵ Pa/m, while at an air flow rate of 48.96 Nm³/h the worncatalyst particles, after 360 tests, exhibited a flow resistance of1.22×10⁵ Pa/m.

EXAMPLE 3

The procedure of Example 1 was followed using 2.06 kg of nickel onα-alumina support catalyst balls of nominal diameter 6 mm from Dycat,Type 54/98. This catalyst support material is much more friable thanthat used in Examples 1 and 2 with only about 25% of the crush strengthof the catalyst used in Examples 1 and 2. The weight of the catalyst waschecked after 10, 60, 150, 300 and 390 tests and showed a total weightloss of 7.0% over 390 tests. During the tests catalyst fragmentsrepresented by this weight loss were visibly removed from the bed by thegas flow as dust. The amount lost in each group of tests decreased asfollows, expressed as average weight % lost per lift and drop cycle:0.085, 0.042, 0.026, 0.010, 0.009.

EXAMPLE 4

In separate tests in the same apparatus as was used in Examples 1 to 3the flow resistance of the fresh catalyst particles and of the worncatalyst particles, after 390 tests, was compared. At an air flow rateof 49.67 Nm³/h the fresh catalyst particles exhibited a pressure loss of1.15×10⁵ Pa/m, while at an air flow rate of 49.77 Nm³/h the worncatalyst particles exhibited a-pressure loss of 1.32×10⁵ Pa/m. Theincrease in pressure loss can be attributed to be due mainly to thereduced voidage (measured as 0.462 fresh and 0.449 worn) and the reducedsize of the worn particles (which was estimated to be equivalent to areduction in diameter, compared to the fresh catalyst particles, of 2%).This Example demonstrates that, because the process substantiallyremoves the fines resulting from particle wear, the process allows thepressure drop in operation to remain as low as can be practicallyexpected.

1. A process in which an elastic fluid is contacted with a particulatesolid, which process comprises the steps of: (a) providing asubstantially vertical elongate tubular containment zone containing acharge of the particulate solid, the volume of the containment zonebeing greater than the settled volume of the charge of the particulatesolid; (b) providing upper retainer means mounted at the upper end ofthe containment zone, the upper retainer means being permeable to thefluid but adapted to retain particulate solid in the containment zone,and follower means movably mounted in the containment zone beneath thecharge of particulate solid for movement upwardly from the lower end ofthe containment zone upon upward flow of elastic fluid through thecontainment zone at a rate beyond a threshold rate; and (c) causing theelastic fluid to flow upwardly through the containment zone at a ratewhich is sufficient to cause particulate solid to rise up towards theupper end of the containment zone and form a cushion of particulatesolid against the underside of the upper retainer means and which is inexcess of the threshold rate so as to cause the follower means to moveupwardly until it abuts against the underside of the cushion ofparticulate solid.
 2. A process according to claim 1, wherein theelongate containment zone is one of a plurality of elongate containmentzones connected in parallel.
 3. A process according to claim 1, whereinat least part of said containment zone is of substantially uniformhorizontal cross-section.
 4. A process according to claim 3, wherein atleast part of said containment zone comprises a tube of substantiallycircular cross section.
 5. A process according to claim 4, wherein atleast part of said containment zone comprises a tube having an internaldiameter of about 6 inches (about 15.2 cm) or less.
 6. A processaccording to claim 3, wherein at least part of said containment zonecomprises a tube having an internal diameter of about 2 inches (about5.08 cm) or less.
 7. A process according to claim 1, wherein saidfollower means is arranged to block passage of elastic fluid up or downthe containment zone apart from through a clearance gap between theinternal surface of the containment zone and the follower means, theclearance gap having a width less than the smallest dimension of anon-fragmented particle of the particulate solid.
 8. A process accordingto claim 7, wherein said follower means comprises a closed lower endportion for defining the gap means and an upper portion provided withelastic fluid passing means.
 9. A process according to claim 1, whereinsaid elastic fluid passing means comprises a plurality of substantiallyconcentric rings spaced one from another, the clearance between adjacentrings being less than the smallest dimension of a non-fragmentedparticle of the particulate solid.
 10. A process according to claim 1,wherein said containment zone contains a plurality of types ofparticulate solid, each type being separated from an adjacent type bymeans of a respective follower means.
 11. A process according to claim1, wherein said particulate solid has at least one dimension less thanabout 10 mm.
 12. A process according to claim 1, wherein saidparticulate solid is substantially spherical in shape.
 13. A processaccording to claim 1, wherein said particulate solid comprises acatalyst.
 14. A process according to claim 1, wherein after initialloading of the particulate solid, the pressure drop across thecontainment zone is measured in a measurement step.
 15. A processaccording to claim 14, wherein particulate solid is added to or removedfrom the containment zone if the pressure drop measured does not conformto a predetermined value.
 16. A process according to claim 14, whereinafter initial loading of the particulate solid but prior to themeasurement step elastic fluid is caused to flow upwardly through thecontainment zone at a rate in excess of the threshold rate so as tocause the particulate solid to form a cushion of particulate solidagainst the underside of the upper retainer and so as to cause thefollower means to rise up the containment zone until it abuts againstthe underside of the cushion of particulate solid, and thereafter theupward flow of elastic fluid is reduced or discontinued so as to permitformation of a settled bed of particulate solid.
 17. A process accordingto claim 1, wherein after initial loading of the particulate solid thesettled volume of particulate solid in the containment zone is measuredin a measurement step.
 18. A process according to claim 17, whereinparticulate solid is added to or removed from the containment zone ifthe settled volume of particulate solid in the containment zone does notconform to a predetermined value.
 19. A process according to claim 1,wherein the particulate solid is a catalyst effective for catalysing adesired chemical reaction, and wherein an elastic fluid comprising areaction feed mixture capable of undergoing the desired chemicalreaction is passed in upflow mode through the containment zone.
 20. Aprocess according to claim 19, wherein said containment zone and saidparticulate solid are subjected to a temperature of at least about 500°C.
 21. A process according to claim 20, wherein said desired chemicalreaction is a partial oxidation reaction, wherein said elastic fluidcomprises a partial oxidation feed mixture, wherein said particulatesolid is a partial oxidation catalyst, and wherein the temperature ofthe containment zone and the partial oxidation catalyst is maintained bysaid partial oxidation reaction.
 22. A process according to claim 20,wherein said desired chemical reaction is a steam reforming reaction,wherein said elastic fluid comprises a steam reforming feed mixture,wherein said particulate solid is a steam reforming catalyst, andwherein the temperature of the containment zone and the steam reformingcatalyst is maintained by hot combustion gases external to saidcontainment zone.
 23. A process according to claim 1, wherein theparticulate solid is a catalyst effective for catalysing a desiredchemical reaction, and wherein an elastic fluid comprising a reactionfeed mixture capable of undergoing the desired chemical reaction ispassed in downflow mode through the containment zone.
 24. Apparatus foreffecting contact of an elastic fluid with a particulate solidcomprising: (a) reactor means defining a substantially vertical elongatetubular containment zone for containing a charge of the particulatesolid, the volume of the containment zone being greater than the settledvolume of the particulate solid, the containment zone having an upperend and a lower end, and the reactor means being mounted so that theupper end of the containment zone lies above the lower end of thecontainment zone; (b) upper retainer means mounted at the upper end ofthe containment zone, the upper retainer means being permeable to thefluid but adapted to retain particulate solid in the containment zone;and (c) follower means movably mounted in the containment zone beneaththe charge of particulate solid, the follower means being constructedand arranged within the containment zone so that it rises upwardly upthe containment zone solely under the pressure exerted by the elasticfluid when the upward flow rate of elastic fluid is greater than athreshold flow rate until it abuts against the cushion of particulatesolid.
 25. Apparatus according to claim 24, wherein the elongatecontainment zone is one of a plurality of elongate containment zonesconnected in parallel.
 26. Apparatus according to claim 24, wherein atleast part of said containment zone is of uniform horizontalcross-section.
 27. Apparatus according to claim 26, wherein at leastpart of said containment zone comprises a tube of substantially circularcross section.
 28. Apparatus according to claim 27, wherein at leastpart of said containment zone comprises a tube having an internaldiameter of about 6 inches (about 15.2 cm) or less.
 29. Apparatusaccording to claim 27, wherein at least part of said containment zonecomprises a tube having an internal diameter of about 2 inches (about5.08 cm) or less.
 30. Apparatus according to claim 24, wherein saidfollower means is arranged to block passage of elastic fluid up or downthe containment zone apart from through a clearance gap between theinternal surface of the containment zone and the follower means, theclearance gap having a width less than the smallest dimension of anon-fragmented particle of the particulate solid.
 31. Apparatusaccording to claim 30, wherein said follower means comprises a closedlower end portion for defining the gap means and an upper portionprovided with elastic fluid passing means.
 32. Apparatus according toclaim 31, wherein said elastic fluid passing means comprises a pluralityof substantially concentric rings spaced one from another, the spacingbetween adjacent rings being less than the smallest dimension of anon-fragmented particle of the particulate solid.
 33. Apparatusaccording to claim 24, wherein said containment zone is adapted forcontaining a plurality of types of particulate solid, each type beingseparated from an adjacent type by means of a respective follower means.34. Apparatus according to claim 24, wherein the particulate solid is acatalyst effective for catalysing a desired chemical reaction, furtherincluding means for passing an elastic fluid comprising a reaction feedmixture capable of undergoing the desired chemical reaction in upflowmode through the containment zone.
 35. Apparatus according to claim 24,wherein the particulate solid is a catalyst effective for catalysing adesired chemical reaction, further including means for passing anelastic fluid comprising a reaction feed mixture capable of undergoingthe desired chemical reaction in downflow mode through the containmentzone.
 36. A method of loading a particulate solid into a substantiallyvertical tube in readiness for conducting a method in which an elasticfluid is contacted with the particulate solid, which method comprisesthe steps of: (a) providing a substantially vertical elongate tubularreactor having an elongate containment zone for containing a charge of aparticulate solid; (b) providing at the lower end of the containmentzone follower means movably mounted in the containment zone for movementupwardly from the lower end of the containment zone upon upward flow ofelastic fluid through the containment zone at a rate beyond a thresholdrate; (c) loading a predetermined charge of the particulate solid intothe containment zone on top of the follower means to provide a settledvolume of the particulate solid that is less than the volume of thecontainment zone; (d) mounting at the upper end of the containment zoneupper retainer means permeable to the fluid but adapted to retainparticulate solid in the containment zone; and (e) causing an elasticfluid to flow upwardly through the containment zone at a rate which issufficient to cause particulate solid to rise up towards the upper endof the containment zone and form a cushion of particulate solid againstthe underside of the upper retainer means and which is in excess of thethreshold rate so as to cause the follower means to move upwardly untilit abuts against the underside of the cushion of particulate solid. 37.A method according to claim 36, wherein the elongate containment zone isone of a plurality of elongate containment zones connected in parallel.38. A method according to claim 36, wherein said containment zone is ofuniform horizontal cross-section.
 39. A method according to claim 38,wherein at least part of said containment zone comprises a tube ofsubstantially circular cross section.
 40. A method according to claim39, wherein at least part of said containment zone comprises a tubehaving an internal diameter of about 6 inches (about 15.2 cm) or less.41. A method according to claim 39, wherein at least part of saidcontainment zone comprises a tube having an internal diameter of about 2inches (about 5.08 cm) or less.
 42. A method according to claim 36,wherein said follower means is arranged to block passage of elasticfluid up or down the containment zone apart from through gap meansbetween the internal surface of the containment zone and the followermeans, the gap means having a width less than the smallest dimension ofa non-fragmented particle of the particulate solid.
 43. A methodaccording to claim 42, wherein said follower means comprises a closedlower end portion for defining the gap means and an upper portionprovided with elastic fluid passing means.
 44. A method according toclaim 36, wherein said elastic fluid passing means comprises a pluralityof substantially concentric rings spaced one from another, the clearancebetween adjacent rings being less than the smallest dimension of anon-fragmented particle of the particulate solid.
 45. A method accordingto claim 36, wherein said particulate solid has at least one dimensionless than about 10 mm.
 46. A method according to claim 36, wherein saidparticulate solid is substantially spherical in shape.
 47. A methodaccording to claim 36, wherein said particulate solid comprises acatalyst.
 48. A method according to claim 36, wherein the settled volumeof particulate solid in the containment zone is measured in ameasurement step.
 49. A method according to claim 48, whereinparticulate solid is added to or removed from the containment zone ifthe settled volume of particulate solid in the containment zone does notconform to a predetermined value.
 50. A method according to claim 36,wherein the method includes the following steps: (f) measuring thepressure drop across the containment zone in a measurement step; and (g)comparing the measured pressure drop with a design value.
 51. A methodaccording to claim 50, wherein particulate solid is added to or removedfrom the containment zone if the measured pressure drop does not conformto the design value, whereafter the pressure drop is measured again. 52.A method according to claim 49, wherein after initial loading of theparticulate solid but prior to the measurement step elastic fluid iscaused to flow upwardly through the containment zone at a rate in excessof the threshold rate so as to cause the particulate solid to form acushion of particulate solid against the underside of the upper retainermeans and so as to cause the follower means to move upwardly until itabuts against the underside of the cushion of particulate solid, andthereafter the upward flow of elastic fluid is discontinued so as topermit formation of a settled bed of particulate solid.
 53. A methodaccording to claim 36, wherein said particulate solid is selected from apartial oxidation catalyst and a steam reforming catalyst.
 54. A methodaccording to claim 36, wherein in step (e) the upward flow of elasticfluid is maintained for a period and at a rate sufficient to causesubstantially all particles which are smaller than a predetermineddesign particle size and are sufficiently small to pass through theupper retainer means to pass through the upper retainer means.